This invention relates generally to semiconductor memories and, particularly, to schemes for repairing bad memory locations in semiconductor memories.
Conventionally, redundancy may be provided for semiconductor memories to replace bad memory locations with good redundant memory locations. In this way, it is not necessary to discard the entire semiconductor memory just because some number of rows, columns, or cells within the memory have bad memory locations. This dramatically increases the yield of conventional semiconductor memories. For example, some memories, such as flash memories, may include redundant rows, which are extra rows within an erase block that can be used to replace defective rows within the same erase block. Similarly, redundant columns are extra columns within an erase block that can be used to replace defective columns within the same erase block. Likewise, redundant blocks are extra erase blocks on a flash device that can be used to replace defective blocks that cannot be repaired with column and/or row redundancy.
Most schemes provide multiple types of redundant elements (e.g. one scheme would have redundant rows and redundant columns. Another scheme might have redundant segments and redundant rows). However, each of these redundancy schemes is limited to a specific type of defect. Thus, some schemes may provide block redundancy, other schemes provide row redundancy, and still other schemes provide column redundancy. To the extent that the defect does not fit well within to the available fixed redundancy scheme, it may be awkward or impossible to provide adequate remediation.
Thus, there is a need for more flexible ways to provide redundancy for semiconductor memories.